1. Field of the Invention
This invention relates to a device and method for moving a first bone segment relative to a second bone segment to externally fix and stabilize bone fractures and to correct bone deformities. More particularly, this device provides an arc gear member which is attached to the first bone segment and a drive means which is attached to the second bone segment and which moves the first bone segment through an arc shaped path to place it in the desired position relative to the second bone segment.
2. Description of the Related Art
The present invention relates to a device for externally fixing and stabilizing bone fractures and correcting bone deformities. A number of devices for external corrections and setting of broken bones have been proposed with some models available on the market. With external fixation, generally, a first set of pins or wires are passed through the skin and soft tissues into the bone above the fracture or deformity and a second set of pins or wires are likewise inserted into the bone below the fracture or deformity. An external device is then connected to the sets of pins or wires to maintain the bone segments in the proper position. Also, there are a number of external devices including hinges, universal joints and ball joints which provide for moving the bone segments in relation to each other to achieve a more natural shape.
When alignment of bone segments is required, it is often desirable to move the bone segments slowly, over a period of several days to months, into the desired positions. This allows live bone cells, blood vessels, etc. located between the bone segments to continue to live and function, providing a stronger, more natural union upon complete correction. This alignment of bone segments is usually accompanied by either a corticotomy or osteotomy. A corticotomy consists of the removal of just the hard outer cortex of the bone while preserving periosteal and endosteal blood supplies. A corticotomy is generally sufficient for small to moderate bone movement. More significant bone movement may require an osteotomy wherein the bone is cut and removed to a greater extent. This method of slowly moving bone segments, over time, into the correct position is generally known as the Ilizarov method. When this slow movement is required, it is desirable that the motion be driven mechanically and that the drive mechanism be integral with the external brace such that medical personnel or the patient can easily and accurately move the bone segments.
Generally, when bone segments are required to be moved relative to each other, there are four types of movement: angular, rotational, translational-extension or compression, and translational-lateral.
There are a number of external devices which provide for at least some type of slow movement of bone segments relative to each other. Many of these devices provide for only one or two types of movements noted above. Other devices, such as, for example those shown in U.S. Pat. Nos. 4,033,340 and 4,488,542, provide for more complex movement.
There are several shortcomings associated with the known devices. First, many devices exist which provide for relatively simple movement of bone segments, e.g., translational-extension. Generally, these devices function satisfactorily for simple movement, however, many of the bone placement corrections require more complex movements than these devices can provide.
The devices which can provide more complex movement also suffer significant shortcomings. One such shortcoming is that these devices often require a "staged method" where one type of movement is made, then another type, in a stepwise, staged fashion. An example of the staged method would be first correcting the rotational movement, then correcting the translational movement, and finally correcting the angular movement. This is less desirable than the "one motion method" which simultaneously corrects for several or all types of motion. The staged method generally takes more time and therefore results in more discomfort, stress and trauma to the patient.
Another shortcoming with the known devices is that the placement of the device is often not very exact. Generally, more complex corrections are made by determining the plane of deformity and the required movement within that plane. Known devices do not provide an adequate means for aligning and positioning the device in the optimum position. Thus, often the optimum correction is not made or additional corrective steps are required.
Further, upon x-raying, the known devices can significantly block the view of the bone segments. Additionally, the known devices are often bulky and difficult to operate, thus adding error, weight and extra work to the application of the device.
Thus, there exists the need for a compact, non-obstructive external fixation device capable of moving two bone segments relative to each other through a vast range of complex corrective movements while allowing easy, accurate alignment and placement of the device.